1. Field of the Invention
The present invention relates to photosensitive compounds that generate free radicals upon exposure to light. More particularly, it relates to derivatives of halomethyl-1,3,5-triazines.
2. Discussion of the Prior Art
Compounds that decompose to generate free radicals (free radical generating agents) upon exposure to light are well known in the graphic arts. Organic halogen compounds, which are capable of generating free radicals such as a chlorine free radical or a bromine free radical upon exposure to light, have been widely used as photoinitiators in photopolymerizable compositions, as photoactivators in free radical photographic compositions, and as photoinitiators for reactions catalyzed by acids formed by light. The spectral sensitivity of these compositions may be broadened by the addition of sensitizers which in essence transfer their absorbed energy to the organic halogen compound. The use of such halogen compounds in photopolymerization processes and free radical photographic processes have been described in Kosar., Light-Sensitive Systems, J. Wiley & Sons (New York 1965), pp. 180-181, 361-370.
Halomethyl-1,3,5-triazines are known to be initiators for a number of photochemical reactions. They can be employed to produce free radicals by actinic radiation for initiating polymerization or color changes and for initiating secondary reactions upon liberation of acid by the interaction of the free-radicals when hydrogen donors are present.
Examples of the use of the halomethyl-1,3,5-triazines in the free radical polymerization of acrylate monomers are described in U.S. Pat. Nos. 3,905,815; 3,617,288; 4,181,752; 4,391,687; 4,476,215; and DE 3,517,440. U.S. Pat. No. 3,779,778 discloses the photoinitiated acid catalyzed decomposition of pyranyl ether derivatives to produce photosolubilizable compositions useful as positive printing plates. Chromophore substituted styryl-1,3,5-triazines and their uses are disclosed in U.S. Pat. No. 3,987,037 and U.S. Pat. No. 3,954,475. Radiation sensitive compositions containing bi- and polyaromatic substituted triazines are disclosed in U.S. Pat. No. 4,189,323.
Co-initiators usually comprise two compounds, a light-sensitive compound usually identified as a photoinitiator, and an activator or additive compound which in the presence of the photoinitiator is not significantly directly excited by the activating radiation, but instead forms a free radical in response to the exposure of the photoinitiator. Known classes of such additives include amines, sulfinic acids and sulfinic acid esters, sulfones, alpha- and beta-dicarbonyl compounds, such as bornanedione and acetylacetone, phosphines, phosphites, and stannates.
An effective system which consists of an amine and an aromatic carbonyl compound is Michler's ketone and benzophenone as described in U.S. Pat. No. 3,682,641. A number of aromatic carbonyl compounds have been disclosed as being useful with amine additives to form co-initiators of many kinds. Such mixtures are described by Ledwith, J. Oil Col. Chem. Assoc. 1976, 59, 167. These compounds include phenones, including cyclic ketones such as benzophenone, fluorenones, anthraquinones, and anthranones. More recently, 3-keto-coumarins have been shown to be effective with Michler's ketone, as described in U.S. Pat. No. 4,366,228 and have been highly effective in photopolymerization compositions of various kinds. Other examples of similar systems are described in U.S. Pat. Nos. 3,488,269; 3,966,573; 3,933,682; 3,729,404; 3,1573,922; and 3,650,927.